Preparation of palladium film by coating photolysis process using KrF or ArF excimer laser

The preparation of palladium (Pd) films has been investigated using KrF or ArF laser irradiation on a Pd acetate (PdAc) coated substrate. A crystalline Pd film could be obtained by KrF laser irradiation (fluence = 15-40 mJ/cm²) but PdAc was found to remain in the film. An increase in the substrate temperature to 423 K decreased the inclusion of the unreacted precursor and produced a better crystallinity. An amorphous and uniform Pd film composed of very fine particles was found to be formed by this process under reduced pressure, which is probably due to the preferential ablation of the crystalline nuclei. ArF laser irradiation is more effective for decomposing the PdAc and for producing a Pd film with a better crystallinity and no (or smaller) organic inclusion.     

Influence of the laser wavelength on the epitaxial growth and electrical properties of La0.8Sr0.2MnO3 films grown by excimer laser-assisted MOD

Epitaxial La_1−xSr_xMnO₃ (LSMO) films were prepared by excimer laser-assisted metal organic deposition (ELAMOD) at a low temperature using ArF, KrF, and XeCl excimer lasers. Cross-section transmission electron microscopy (XTEM) observations confirmed the epitaxial growth and homogeneity of the LSMO film on a SrTiO₃ (STO) substrate, which was prepared using ArF, KrF, and XeCl excimer lasers. It was found that uniform epitaxial films could be grown at 500 °C by laser irradiation. When an XeCl laser was used, an epitaxial film was formed on the STO substrate at a fluence range from 80 to 140 mJ/cm² of the laser fluence for the epitaxial growth of LSMO film on STO substrate was changed. When the LaAlO₃ (LAO) substrate was used, an epitaxial film was only obtained by ArF laser irradiation, and no epitaxial film was obtained using the KrF and XeCl lasers. When the back of the amorphous LSMO film on an LAO substrate was irradiated using a KrF laser, no epitaxial film formed. Based on the effect of the wavelength and substrate material on the epitaxial growth, formation of the epitaxial film would be found to be photo thermal reaction and photochemical reaction. The maximum temperature coefficient of resistance (TCR) of the epitaxial La_0.8Sr_0.2MnO₃ film on an STO substrate grown using an XeCl laser is 4.0%/K at 275 K. XeCl lasers that deliver stabilized pulse energies can be used to prepare LSMO films with good a TCR.     

Excimer gas-discharge tunable ArF laser

Intense laser oscillation has been observed from ArF molecules at 1933 Å. Excitation of the gas mixture NF₃:Ar:He=1:55:630 at total pressures above 2.1 atm was produced by a transverse electric discharge. The range of fine tuning was from 1927 Å to 1936 Å. An output energy of 0.8 mJ was measured from a laser pulse 15 ns in duration.     

Output and picosecond amplification characteristics of an efficient and high-power discharge excimer laser

Improvements in output pulse energy and efficiency of a conventional capacitor-transfer-type discharge excimer laser with automatic preionization have been achieved by extending the discharge volume and resulting moderate pumping of the active medium. The discharge laser produces a pulse energy of more than 1 J for XeCl, KrF, and ArF lasers in square beams of about 2×2 cm², and the maximum overall efficiency observed is 2.9% for XeCl, 3.2% for KrF and 1.8% for ArF. The laser device has been involved in a picosecond ( 32 ps) XeCl laser amplification system, and was operated as an amplifier at a repetitive frequency of 10 Hz. Saturation fluence for XeCl laser was measured to be 1.4 mJ/cm², and the picosecond pulse energy of 40 mJ was extracted from the amplifier.On leave from Ebara Corp., 6-6-7, Ginza, Chuo-ku, Tokyo 104, JapanOn leave from Mitsubishi Heavy Industries, LTD., 4-6-22, Kan-on shinmachi, Nishi-ku, Hiroshima 733, Japan     

Temporal extension of stable glow discharges in fluorine-based excimer laser gas mixtures by the addition of xenon

The effect of addition of xenon on the long term homogeneity of discharges in F₂and ArF excimer laser gas mixtures was investigated in a small-volume discharge chamber. The gas mixture in the discharge chamber was preionized by X-rays. A special electrical excitation circuit containing a pulse forming line provided a long, square-shaped current pumping pulse of a predetermined duration to the discharge electrodes. The initiation and the development of the discharge was monitored via its fluorescence signal with an intensified CCD camera. We found that adding Xe up to partial pressures of 0.53 mbar extended the homogeneous phase of the discharge from 80 ns to approximately 200 ns in He/F₂as well as in He/Ar/F₂and Ne/Ar/F₂excimer laser gas mixtures. Monitoring of the ArF and XeF spontaneous emission signals showed that the formation of ArF excimers remained unaffected by the addition of xenon (up to 1.3 mbar) to the laser gas mixture.     

Preparation of Y2O3:Eu thin films by excimer-laser-assisted metal organic deposition

Europium-doped yttrium oxide (Y₂O₃:Eu) thin films were successfully deposited on quartz and ITO/glass substrates by excimer-laser-assisted metal organic deposition (ELAMOD) at low temperatures. The effects of laser wavelength and thermal temperature on the films’ crystallinity and photoluminescence properties were investigated. Films irradiated by an ArF laser at 80 mJ/cm² and 400–500°C were highly crystallized compared with those prepared by thermal MOD. In contrast, when the film was irradiated by a KrF laser at 500°C, no crystalline Y₂O₃:Eu was formed. The Y₂O₃:Eu film irradiated by the ArF laser at 80 mJ/cm² and 500°C showed typical PL spectra of Eu³⁺ ions with cubic symmetry and a ⁵D₀→⁷F₂ transition at ∼612 nm. The PL intensity at 612 nm was much higher for the film prepared with ELAMOD than for that prepared by the thermal-assisted process, and the photoemission intensity of the film prepared with ELAMOD strongly depended on the substrate material.     

Dual-beam ablation of fused silica by multiwavelength excitation process using KrF excimer and F2 lasers

A new technique of dual-beam laser ablation of fused silica by multiwavelength excitation process using a 248-nm KrF excimer laser (ablation beam) coupled with a 157-nm F₂ laser (excitation beam) in dry nitrogen atmosphere is reported. The dual-beam laser ablation greatly reduced debris deposition and, thus, significantly improved the ablation quality compared with single-beam ablation of the KrF laser. High-quality ablation can be achieved at the delay times of KrF excimer laser irradiation shorter than 10 ns due to a large excited-state absorption. The ablation rate can reach up to 80 nm/pulse at the fluence of 4.0 J/cm² for the 248-nm laser and 60 mJ/cm² for the F₂ laser. The ablation threshold and effective absorption coefficient of KrF excimer laser are estimated to be 1.4 J/cm² and 1.2᎒⁵ cm^-1, respectively.     

Pulsed blue-light generation by the frequency doubling of the 4F3/2 to 4I9/2 transition in Nd:YAG and Nd:YAlO3

We report on the frequency doubling of Q-switchedNd:YAG and Nd:YAlO₃ lasers emitting at 946 and 930 nm, respectively (⁴F_3/2 to ⁴I_9/2 transition). The neodymium-doped laser host crystals were excited with a flashlamp-pumped Cr:LiSAF laser operating in a free-running mode. Blue-light pulses were obtained at both 473 nm (9 mJ, 25 ns FWHM) and 465 nm (4.4 mJ, 35 ns FWHM) by using a potassium niobate crystal as an extra-cavity frequency doubler. The second-harmonic generation conversion efficiencies reached 53% and 31%, respectively. Received: 23 June 1999 / Revised version: 8 August 1999 / Published online: 3 November 1999     

Permanent holographic recording in indium oxide thin films using 193 nm excimer laser radiation

Permanent holographic recording in sputtered indium oxide (InO_x) thin films is demonstrated, using ultraviolet radiation at 193 nm emitted by an ArF excimer laser. Steady-state refractive index changes of up to 5×10^-3 are calculated from the measured diffraction efficiency of a HeNe laser probe beam. The recorded gratings exhibit a dynamic behaviour that relaxes to a steady-state value that depends on the oxygen partial pressure used during growth and on the recording beam intensity. The observed behaviour is explained in terms of laser-induced structural changes. Received: 12 October 1998 / Accepted: 8 March 1999 / Published online: 4 August 1999     

Pulsed inductive discharge CO2 laser

A pulsed inductive discharge CO₂ laser with a wavelength of 10.6 μm has been created for the first time. The excitation system of a cylindrical pulsed inductive discharge (pulsed inductively coupled plasma) in the gas mixture of CO₂:N₂:He was developed. The temporal and energy parameters of the laser radiation were investigated. The maximum inductive discharge CO₂ laser radiation energy of 104 mJ was achieved. An average power of 3.2 W was obtained at laser generation energy of 65 mJ and pulse repetition rate of 50 Hz. In the cross-section, the laser radiation had the ring shape with an external diameter of 34 mm and thickness of 4-5 mm. The measured divergence of laser radiation was 12 mrad.     

Influence of laser fluence and irradiation timing of F2 laser on ablation properties of fused silica in F2-KrF excimer laser multi-wavelength excitation process

A collinear irradiation system of F₂ and KrF excimer lasers for high-quality and high-efficiency ablation of hard materials by the F₂ and KrF excimer lasers’ multi-wavelength excitation process has been developed. This system achieves well-defined micropatterning of fused silica with little thermal influence and little debris deposition. In addition, the dependence of ablation rate on various conditions such as laser fluence, irradiation timing of each laser beam, and pulse number is examined to investigate the role of the F₂ laser in this process. The multi-wavelength excitation effect is strongly affected by the irradiation timing, and an extremely high ablation rate of over 30 nm/pulse is obtained between -10 ns and 10 ns of the delay time of F₂ laser irradiation. The KrF excimer laser ablation threshold decreases and its effective absorption coefficient increases with increasing F₂ laser fluence. Moreover, the ablation rate shows a linear increase with the logarithm of KrF excimer laser fluence when the F₂ laser is simultaneously irradiated, while single KrF excimer laser ablation shows a nonlinear increase. The ablation mechanism is discussed based on these results. Received: 16 July 2001 / Accepted: 27 July 2001 / Published online: 2 October 2001     

Emission characteristics of plasma of a transverse volume discharge in mixtures of helium, argon, and krypton with sulfur hexafluoride

The emission characteristics of the plasma of repetitively pulsed spontaneous UV-VUV radiation sources on the basis of ArF* (193 nm) and KrF* (249 nm) molecules, and the products of decomposition of sulfur hexafluoride molecules pumped by a transverse volume discharge in a mixture of inert gases with sulfur hexafluoride molecules have been investigated. The discharge emission spectra in the range of 190–780 nm at the low-current and high-current stages of the transverse discharge, the time characteristics of the voltage across the electrodes, the pump current, and the emission of excimer molecules and the products of decomposition of sulfur hexafluoride have been studied. It is shown that, in the gas-static operation mode of the radiator at the number of discharge pulses smaller than 10³, the 193-nm ArF* and 249-nm KrF* bands are main in the emission spectrum. Upon further operation of the radiator, a spectral continuum is formed on the basis of sulfur molecular bands in the range 260–550 nm.     

ArF准分子激光振荡放大系统的研究

研究了ＡｒＦ准分子激光振荡放大系统，中心波长１９３ｎｍ，用一只闸流管作为开关元件，通过主充放电网络匹配，有效地解决了两台器件的放电抖动，振荡放在倍数达到约５０倍，系统单脉冲输出能量５０ｍＪ，光束发射角低于０．２０ｍｒａｄ。     

0.73 J脉冲能量KrF准分子激光器的特性

研制了一台KrF大能量准分子激光器,激光器采用紧凑型Chang电极与紫外火花预电离的结合, 实现了激活区大面积的均匀辉光放电,利用LC反转倍压以及一级磁脉冲压缩技术在放电电容上实现了峰值电压40 kV、脉冲上升时间约为100 ns的高压快脉冲激励。研究了工作气体含量对激光器能量输出的影响,在总气压3.3105 Pa,F2/He, Kr, Ne体积分数比值为1.97∶3.18∶94.85,充电电压27 kV时,得到了738 mJ的单脉冲能量输出,激光近场光斑30 mm14 mm,在充电电压23 kV时,全电效率最高,达到2.0%。     

Pulsed X-ray diode with a long-lifetime plasma cathode

6 shots, the X-ray dose, uniformity, and ionisation rate values guarantee an effective preionisation of excimer laser discharges. Owing to both the long lifetime and the substantial absence of maintenance, this X-ray diode seems suitable to preionise commercial gas lasers, such as excimer and TEA CO₂ lasers. Received: 28 August 1998 / Revised version: 16 November 1998 / Published online: 24 February 1999     

Laser-based techniques for living cell pattern formation

In the production of biosensors or artificial tissues a basic step is the immobilization of living cells along the required pattern. In this paper the ability of some promising laser-based methods to influence the interaction between cells and various surfaces is presented. In the first set of experiments laser-induced patterned photochemical modification of polymer foils was used to achieve guided adherence and growth of cells to the modified areas: (a) Polytetrafluoroethylene was irradiated with ArF excimer laser (λ=193 nm, FWHM=20 ns, F=9 mJ/cm²) in presence of triethylene–tetramine liquid photoreagent; (b) a thin carbon layer was produced by KrF excimer laser (λ=248 nm, FWHM=30 ns, F=35 mJ/cm²) irradiation on polyimide surface to influence the cell adherence. It was found that the incorporation of amine groups in the PTFE polymer chain instead of the fluorine atoms can both promote and prevent the adherence of living cells (depending on the applied cell types) on the treated surfaces, while the laser generated carbon layer on polyimide surface did not effectively improve adherence. Our attempts to influence the cell adherence by morphological modifications created by ArF laser irradiation onto polyethylene–terephtalate surface showed a surface–roughness dependence. This method was effective only when the Ra roughness parameter of the developed structure did not exceed the 0.1 micrometer value. Pulsed laser deposition with femtosecond KrF excimer lasers (F=2.2 J/cm²) was effectively used to deposit structured thin films from biomaterials (endothelial cell growth supplement and collagen embedded in starch matrix) to promote the adherence and growth of cells. These results present evidence that some surface can be successfully altered to induce guided cell growth.     

Generation of short-pulse VUV and XUV radiation

Starting from intense short-pulse KrF (248 nm, 25 mJ, 400 fs), ArF (193 nm, 10 mJ, 1 ps), and Ti:sapphire (810 nm, 100 mJ, 150 fs) laser systems, schemes for the generation of fixed-frequency and tunable VUV and XUV radiation by nonlinear optical techniques are investigated. With the KrF system, a four-wave mixing process in xenon yields tunable radiation in the range of 130–200 nm with output energies of, so far, 100 J in less than 1 ps. For the XUV spectral range below 100 nm, nonperturbative high-order harmonic generation and frequency mixing processes in noble gas jets are considered. To achieve tunability, the intense fixed-frequency pump laser radiation is mixed with less intense but broadly tunable radiation from short-pulse dye lasers or optical parametric generator-amplifier systems. In this way, tunability down to wavelengths of less than 40 nm has been demonstrated.     

Laser cleaning of polymer surfaces

We have investigated the removal of small spherical particles from polymer surfaces by means of 193-nm ArF and 248-nm KrF laser light. Polystyrene (PS) particles with diameters in the range of 110 nm to 1700 nm and silica particles (SiO₂) with sizes of 400 nm and 800 nm are successfully removed from two different substrates, polyimide (PI) and polymethylmethacrylate (PMMA). Experiments were performed in air (23 °C, relative humidity 24–28%) and in an environment with a relative humidity (RH) of about 90%. Received: 13 July 2000 / Accepted: 14 July 2000 / Published online: 9 November 2000     

A KrF fast discharge laser in mixtures containing NF3, N2F4 or SF6

A fast discharge KrF laser system (λ = 248.5 nm) has been operated at 25 mJ/pulse, 3.0 MW peak power in high pressure He: Kr: fluoride mixtures containing low concentrations of both krypton and the fluorine donors N₂F₄, NF₃ and SF₆. Lasing action is reported for the first time in N₂F₄ and SF₆ with optimum energy output at 750 and 160 mJ/l respectively.     

Excimer laser-induced diamond graphitization for high-energy nuclear applications

In this work, we have studied the structure and the morphology of a graphite layer induced on the surface of a polycrystalline thermal grade CVD diamond by focusing a pulsed excimer laser operating at KrF (wavelength 248 nm) and ArF (wavelength 193 nm) mixtures. By micro-Raman and photoluminescence spectroscopies, as well as scanning electron microscopy, we reported the synthesis of a turbostratic t-graphite layer after irradiation with ArF laser. By contrast, irradiating with a KrF laser beam, we obtained a disordered graphite layer with 10 laser shots, while 200 consecutive laser pulses resulted in target ablation.